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DIY frame rail reinforcement...

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Old 05-19-2008, 12:55 PM
  #21  
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I've been wondering why more people haven't tried something like this. I was thinking about using angle iron on either side of the rail. Bolt them through the floor and to each other through the rail.
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Old 05-19-2008, 01:02 PM
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Originally Posted by 91NApeewee
thats cool, but the point of the FM rails is that they mount to the floor pans increase the stiffness along them.
Hit the nail on the head here. While these aluminum rails might do something, they certainly won't provide the same rigidity as the FM rails. You really need a hat-shaped section in order to attach top the floor, rather than a C-shaped channel. Remember...the end goal should be closed sections.
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Old 05-19-2008, 01:40 PM
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Originally Posted by Atlanta93LE
Remember...the end goal should be closed sections.
closed sections are not subject to Lateral Torsional Buckling . Damn structural engineering.

But yea, it needs to somehow hold to the floor. Incorporate some L brackets maybe
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Old 05-19-2008, 01:52 PM
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Originally Posted by cueball1
I've been wondering why more people haven't tried something like this. I was thinking about using angle iron on either side of the rail. Bolt them through the floor and to each other through the rail.

I see where you are going with this, but I think the fact that each "half" is tied together benefits you too much to not go with a couple of hat-shaped sections like the FM ones. Wouldn't be that expensive to have a metal fab place shear them up and put them in a brake for four bends. Plus, the will likely be lower weight as well, even without the cutouts on the FM ones. Hell, you can probably hole saw some holes if you want to lower the weight. They are probably saving 2 lbs is all. Bolted wide through the floor is key here.
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Old 05-19-2008, 02:29 PM
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Originally Posted by 91NApeewee
closed sections are not subject to Lateral Torsional Buckling . Damn structural engineering.
Well, they are more resistant to LTB, but they can exhibit that failure mode, especially with highly slender, nonuniform elements. I can show you some photos of it happening if you like

Good to see another structural engineer here. I do structural forensics for a living.
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Old 05-19-2008, 02:45 PM
  #26  
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Originally Posted by Atlanta93LE
Well, they are more resistant to LTB, but they can exhibit that failure mode, especially with highly slender, nonuniform elements. I can show you some photos of it happening if you like

Good to see another structural engineer here. I do structural forensics for a living.
I believe you, lol. I was going off the frame rail lengths not being slender. I assumed their slenderness ratio would not allow LTB to govern.

also, you have a PM
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Old 05-19-2008, 03:02 PM
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Originally Posted by samnavy
How did you hurt your frame rails that bad in the first place?
Low + Speed bumps...mine look like a domestic violence victim.
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Old 05-19-2008, 03:34 PM
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Originally Posted by miatamania
Low + Speed bumps...mine look like a domestic violence victim.
Same here. The driver's side one is really bad.
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Old 05-19-2008, 03:46 PM
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+1 on the lowered vs speedbump problem.
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Old 05-19-2008, 04:02 PM
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Mine suffered when I tried to grind a curb skater style :(
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Old 05-19-2008, 05:07 PM
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ah screw you guys.... every week you disappoint me by making good **** from useless crap :/

kind of makes me want to hang myself for spending all that precious $$ :/
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Old 05-19-2008, 06:12 PM
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Originally Posted by samnavy
What exactly did that entail?
I can see some grinder work and perhaps some hammering. Was it that the rail was slightly wider than the track in the bracing, or was your rail uneven down it's length and you just smoothed it out.

How did you hurt your frame rails that bad in the first place?
What is the width of the rack you're using?

Do you think that these braces would "slip" over an unmolested frame rail?
What would be ideal is if the brace .001" wider than the rail and you would simply tap it up into place with a rubber mallet. Rigging up a crossbrace would be a really simple proposition.

Is there any dramatic difference in the undercarriage between the years. I know FM's brace is "universal", but is there anything to consider along those lines?
1. The massaging was a bit of hammering and a wire wheel. The rail was squished from previous owner probably using it as jacking points...also the rails had a whole bunch of spray undercoating on them (I shipped the car over from Hawaii)
2. Yes they would just slip over if they haden't been so bent outta shape. Light tapping with a rubber mallet worked on another miata that did same project.
3. Pretty sure the undercarriage is similar...the only thing to watch out for is fuel + brake lines.
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Old 05-19-2008, 06:23 PM
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Look into the test method FM did to quantify the stiffness increase from their rails (on their site I believe). Do the same test with your car. Compare results.
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